This invention relates to modular panels for concrete forming structure and connecting members therefor.
In the past, the cost of the formwork needed to erect a poured concrete structure has averaged approximately 50% of the total cost of the concrete structure and one reason for this substantial cost is that the erection of the formwork is labour intensive. Because the cost of labour is high, there is a need for better, more efficient forming systems in order to increase productivity and to reduce the amount of time required to erect formwork. Various attempts have been made in the past to provide a modular forming system that is relatively easy to erect and that is not prohibitively expensive to produce.
Some of the modular panels for concrete formwork in the past have a sheet of plywood or metal that faces the concrete to be poured, which sheet is supported by transverse metal bars or frame members attached to a generally rectangular frame that extends around the perimeter of the panel. Various devices are provided for connecting such panels in a rigid edge-to-edge relationship to create the formwork. One difficulty with these known panels is that they tend to be quite heavy due to the fact that the plywood thickness for such a panel is from 5/8" to 11/16" and the transverse and peripheral frame members can also have a substantial weight, whether made from wood or metal.
It will be appreciated that the ideal modular panel for a concrete forming system should have the greatest possible strength to weight ratio. The panel must have sufficient strength to resist the pressure of the fresh concrete and to prevent bulges in the concrete and they should also be sufficiently strong to withstand the rough handling that they may receive on a construction site. In addition, because these panels are repeatedly assembled, then disassembled, and then moved from one construction site to another for reuse, the smaller the weight of each panel the easier it is to work with. If the weight of the panel is kept to less than 100 pounds, it may be possible to handle and transport the panel by manual labor. Large panels and panels having a weight of 100 pounds or more may neccessitate the use of a crane for handling and transport.
Another difficulty with known panels for formwork is that they are either not suitable for or are costly to use in cold climatic conditions. If no provision is made in the panel for keeping the inside surface of the panel warm, then either the concrete will not cure properly in cold weather, or a special costly enclosure must be created so that the area around the formwork is heated. Although attempts have been made in the past to produce modular panels for formwork that have their own heating means, such attempts have produced panels that are generally unsatisfactory or are too expensive. One difficulty with some of the known heated panels is that they do not stand up very well on a construction site. Often nails must be driven into these panels due to job requirements and such nails can damage known heating systems. Also, if a heating system is to be provided in a modular panel, there should also be insulation in the panel so that heat loss from the panel is not excessive.
U.S. Pat. No. 4,033,544 issued July 5, 1977, to Aluma Building Systems Inc. describes a wall forming structure for a poured concrete wall. Opposed panels are connected together by ties and are supported by strongbacks. Each panel comprises a planar sheathing secured to a plurality of studs that extend parallel to one another. Each strongback comprises a pair of channel-shaped members which are placed in spaced back-to-back relationship. Each of the channel-shaped members has an outwardly facing T-shaped slot for receiving the heads of attachment bolts. A plurality of connecting plates are secured to the strongbacks by these bolts. The difficulty with this known system is that it still requires a considerable amount of labour and time to assemble on a job site. This known system is also not very flexible in that it does not easily accommodate changes in the height or the length of the formwork.
U.S. Pat. No. 3,862,737 issued Jan. 18, 1975 to Hoover Ball and Bearing Company describes a flat panel having a flat surface on one side against which concrete can be poured and having on the other side a U-shaped channel frame extending around the marginal edges of the panel. The panel also has transverse brace members which are secured to the sheet forming the flat surface and at their ends to the U-shaped peripheral frame. Locking devices are inserted through aligned holes in adjacent panels to connect them together. No means are provided for heating these panels which also are not insulated.
U.S. Pat. No. 3,144,701 issued Aug. 18, 1964 to Symons Manufacturing Company describes a panel unit having a rectangular peripheral frame to one side of which is attached a flat rectangular plywood facing. A rectangular rearwardly bulged pan made of high strength sheet material covers the space inside the rectangular frame. In the space between this pan and the plywood facing is a load transferring, heat-insulating material which can be polyether urethane foam. These insulating panels are locked together in a generally conventional fashion using keys and wedges which require that the back of the panel remain open to a substantial extent. Also, the amount of insulation behind any given location on the face of the panel varies considerably. In order to counteract for the lack of insulation at the edges of the panel, this patent specification teaches that one can provide electrical resistance heaters embedded in the marginal portions of the insulation. With this system, it may be difficult for the user to provide the necessary balance between the active heat provided by the heaters and the protection from the cold provided by the passive insulation and therefore the curing of the concrete may not be uniform or adequate.
It is an object of the present invention to overcome or alleviate some of the known problems with the formwork systems and panels of the prior art. The preferred panel described herein has sufficient strength and durability for repeated use on construction sites and its weight can be kept low for ease of handling.
It is another object of the invention to provide a special panel connecting member that can be used in conjunction with tie rods and the preferred panels disclosed herein. This connecting member can be made inexpensively and it is easy to use on the job site. It can come in a number of possible lengths with the length to be used depending upon the particular job application. The connector is designed for use along the edges of the panels and on the outside thereof so that the interior of the panels can be closed and completely insulated.
Another object of the invention is to provide a panel for a concrete forming structure comprising a composite structure made up of flat inner and outer structural sheets that are spaced apart and a structural core that extends between and is rigidly connected to the inner and outer sheets. Resistance to bending and deflection of the panel due to the pressure of fresh concrete is provided by stressing of both the inner and outer sheets when the sheets are subjected to such loads.